Conventional 35 mm film cartridges are normally sold with a portion of the film leader projecting from the exit slot of the cartridge. This allows the camera user to grasp and pull the film for loading in the camera and at the same time provides a visual indication to the camera user that the film in the cartridge is unexposed. Upon rewind, the film is rewound completely into the cartridge and the absence of the protruding leader indicates that the film has been exposed and prevents re-use of the film in a camera thus inherently providing protection against double exposure of the film. Recently, camera and film cartridge designs have been proposed in which the film is totally enclosed in the cartridge when sold. To load the film, the cartridge is inserted and the drive motor operates to thrust the film out of the cartridge to the film take-up spool. Upon rewind, the film is drawn entirely into the cartridge. As a consequence, there is no visual indication to distinguish between an exposed and an unexposed film roll and, thus, numerous camera and cartridge designs have been proposed to provide protection against re-use and double exposure of the film.
It is known, for example, to provide cartridges with mechanical features that cooperate with feelers in the camera that prevent insertion of cartridges into the camera when the film has previously been exposed. In many cases these mechanical features also provide a visual indication of the exposed condition of the film. A representative example of an arrangement providing both visible indication and mechanical lockout means is found in commonly assigned U.S. Pat. No. 5,047,794. U.S. Pat. No. 5,115,268 discloses a mechanical slide on the film cartridge is movable by a cam arrangement upon insertion into the camera to cover the letters UN in the word UNEXPOSED printed on the end of the cartridge to provide a visible indication of an exposed condition of the film in the cartridge. In commonly assigned U.S. Pat. No. 5,032,854 and 5,030,978, a radial bar coded disc on the end of a film cartridge is sensed by an opto-sensor in the camera to position the film spool upon conclusion of rewind at a selected one of plural visual indicators that indicate the exposure condition of film in the camera.
Such arrangements however, require special cartridge designs that add to the cost and complexity of cartridge manufacture. In the case of cartridges with just visual indicators, it is possible to ignore the indicators and load the film into the camera thereby creating a possibility of double exposure of the film.
In commonly assigned co-pending application Ser. No. 08/033,668-Lawther, entitled "Photographic Camera and Film Cartridge with Double Exposure Prevention", word, such as "UnExposed" is imprinted on the side of the cartridge with a normally transparent, thermally responsive material overlying the letters "Un". The cartridge is designed for use in a camera provided with an electrically actuatable heater in the cartridge receiving chamber that is aligned with the thermally responsive material and when the heater is activated upon taking of at least one exposure in the camera, the thermally responsive material is darkened leaving the word "Exposed" as a warning to the user not to reload the cartridge into a camera. A photo detector in the camera senses the opaque condition of the thermally responsive material and sends a signal to the camera controller to prevent loading of the film into the camera. While simpler than the mechanical arrangements described above, it still requires a relatively costly camera design with interface components to activate the thermally responsive material and optically sense the opaque condition of the material.
It is therefore an object of the invention to provide a simple, inexpensive cartridge and camera configuration that provides both a visual indication to the camera user of the exposure condition of photographic film in the cartridge and that also provides the capability of automatically preventing loading of exposed film into the camera to thereby avoid the possibility of double exposing the film in the camera. Moreover, it is an object of the invention to provide a cartridge and camera arrangement with the aforementioned advantages that does not require special, costly interface components in the camera cartridge receiving chamber.